linux-cve-announce - CVE-2025-39962: rxrpc: Fix untrusted unsigned subtract

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Message-ID: <2025100917-CVE-2025-39962-c0e0@gregkh>
Date: Thu,  9 Oct 2025 14:13:17 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-39962: rxrpc: Fix untrusted unsigned subtract

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

rxrpc: Fix untrusted unsigned subtract

Fix the following Smatch static checker warning:

   net/rxrpc/rxgk_app.c:65 rxgk_yfs_decode_ticket()
   warn: untrusted unsigned subtract. 'ticket_len - 10 * 4'

by prechecking the length of what we're trying to extract in two places in
the token and decoding for a response packet.

Also use sizeof() on the struct we're extracting rather specifying the size
numerically to be consistent with the other related statements.

The Linux kernel CVE team has assigned CVE-2025-39962 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.16 with commit 9d1d2b59341f58126a69b51f9f5f8ccb9f12e54a and fixed in 6.16.9 with commit 71571e187106631a8127f2dde780f35caa358d33
	Issue introduced in 6.16 with commit 9d1d2b59341f58126a69b51f9f5f8ccb9f12e54a and fixed in 6.17 with commit 2429a197648178cd4dc930a9d87c13c547460564

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-39962
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/rxrpc/rxgk_app.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/71571e187106631a8127f2dde780f35caa358d33
	https://git.kernel.org/stable/c/2429a197648178cd4dc930a9d87c13c547460564